Writing instrument cap



FIG. 1 is a top, left front perspective view of a writing instrument cap showing my new design;

FIG. 2 is a left side elevational view, the right side being a mirror image thereof;

FIG. 3 is a front elevational view;

FIG. 4 is a bottom plan view; and,

FIG. 5 is a top plan view thereof. 

The ornamental design for a writing instrument cap, as shown and described. 